The present invention relates to electric and electronic detonators and, more specifically, to such detonators being protected against inadvertent firing by stray or induced electrical currents, magnetic fields and the like.
U.S. Pat. No. 5,179,248 (the '248 patent), issued Jan. 12, 1993 to J. Keith Hartman et al. and entitled “Zener Diode For Protection Of Semiconductor Explosive Bridge”, discloses protection of a semiconductor bridge against inadvertent firing by connecting a zener diode across the conductive metal lands forming part of the semiconductor bridge. As explained at column 3, line 14 et seq., a semiconductor bridge device includes a pair of spaced-apart metal lands disposed in ohmic contact on a doped semiconductor layer with a gap between the lands. In response to a voltage or current equal to or in excess of a predetermined level and duration being applied to the gap between the lands, a plasma is formed in the gap with sufficient energy to initiate an explosive disposed in the gap. The device for preventing accidental discharge includes and preferably consists of a zener diode having anode and cathode electrodes respectively connected to the first and second lands of the semiconductor bridge device.
U.S. Pat. No. 5,309,841 (the '841 patent), issued May 10, 1994 to J. Keith Hartman et al. and entitled “Zener Diode For Protection of Integrated Circuit Explosive Bridge”, expands on the disclosure of the '248 patent, including disclosure of circuits adding a capacitor and energy source in parallel with the zener diode and incorporating the elements into an integrated circuit.
As disclosed in both the '248 patent (col. 6, line 56 through col. 7, line 7; FIG. 3) and the '841 patent (col. 7, lines 20-39; FIG. 3), protection against premature firing of the semiconductor explosive bridge is accomplished via waveform clipping by the protective zener diode.
While existing protective schemes for detonator devices may be suitable for their intended purpose, there remains, however, a need in the art for improved protective schemes that provide improved protection against possible stray voltage conditions that could cause unplanned initiation of a detonator.